Biocompatibility in Dental Photopolymer Additive Manufacturing: A Material–Process–Workflow Perspective

Abstract

Direct-printed orthodontic aligners, denture bases and dental prostheses are scaling in clinical use, but the published dental literature has predominantly approached photopolymer biocompatibility from a chemistry-centred perspective. The 2023 REACH SVHC listing of TPO and the subsequent harmonised Repr. Cat. 1B classification under Delegated Regulation (EU) 2024/197 are driving substitution to TPO-free formulations across the European dental segment; chemistry substitution alone does not, by itself, ensure a compliant device-level biological evaluation. This perspective proposes a Material–Process–Workflow framework in which device-level biological performance depends on three interacting engineering variables: material chemistry, cure kinetics governed by the Jacobs working curve, and the post-processing workflow (drain, clean, dry, post-cure), integrated through a formal validation and release step. The three-variable architecture is methodologically related to Quality-by-Design frameworks established in pharmaceutical and medical device manufacturing under the ICH Q8/Q9/Q10 guidance documents; the specific contribution of this perspective is the systematic integration of photopolymer cure kinetics as the central process variable connecting material chemistry to the post-processing workflow and to the device-level validation hierarchy, a connection that has not been developed in the dental photopolymer literature to date. The framework is examined against the peer-reviewed evidence base on dental photopolymer cytotoxicity, post-cure dependence and denture base hydrolytic stability against ISO 20795-1 thresholds. Standardised extractables methodologies and longer-term in vivo clinical follow-up emerge as the principal research priorities for the field through 2030.